Download chapter 5 notes for eighth grade physical science

CHAPTER 5 NOTES FOR EIGHTH GRADE PHYSICAL
SCIENCE
THE OBJECT THAT APPEARS TO STAY IN PLACE IS A REFERENCE POINT.
WHEN AN OBJECT CHANGES POSITON OVER TIME WHEN COMPARED WITH
A REFERENCE POINT, THE OBJECT IS IN MOTION.
THE EARTH'S SURFACE IS A COMMON REFERENCE POINT FOR
DETERMINING POSITION AND MOTION.
THE RATE AT WHICH AN OBJECT MOVES IS ITS SPEED.
THE SI UNIT FOR SPEED IS METERS PER SECOND (M/S).
AVERAGE SPEED= TOTAL DISTANCE/TOTAL TIME.
THE SPEED OF AN OBJECT IN A PARTICULAR DIRECTION IS THE OBJECT'S VELOCITY.
AN OBJECT'S VELOCITY IS CONSTANT ONLY IF ITS SPEED AND DIRECTION DOESN'T CHANGE.
THEREFORE, CONSTANT VELOCITY IS ALWAYS ALONG A STRAIGHT LINE.
CHANGE IN VELOCITY ALSO OCCURS WHEN A BUS CONTINUES TO TRAVEL AT THE SAME SPEED
BUT CHANGES DIRECTION TO TRAVEL A DIFFERENT WAY.
WHEN YOU COMBINE TWO VELOCITIES THAT ARE IN THE SAME DIRECTION, ADD THEM TOGETHER
TO FIND THE RESULTANT VELOCITY.
WHEN YOU COMBINE TWO VELOCITIES THAT ARE IN OPPOSITE DIRECTIONS, SUBTRACT THE
SMALLER VELOCITY FROM THE LARGER VELOCITY. THE RESULTANT VELOCITY IS IN THE DIRECTION
OF THE LARGER VELOCITY.
ACCELERATION IS THE RATE AT WHICH VELOCITY CHANGES.
ACCELERATION= FINAL VELOCITY-STARTING VELOCITY/TIME IT TAKES TO CHANGE VELOCITY.
ACCELERATION IN WHICH VELOCITY INCREASES IS
SOMETIMES CALLED POSITIVE ACCELERATION.
ACCELERATION IN WHICH VELOCITY DECREASES IS SOMETIMES CALLES NEGATIVE ACCELERATION
OR DECELERATION.
A CHANGE IN DIRECTION IS ACCELERATION, EVEN IF THERE IS NO CHANGE IN SPEED.
AN OBJECT TRAVELING IN A CIRCULAR MOTION IS ALWAYS CHANGING ITS DIRECTION. THEREFORE,
ITS VELOCITY IS ALWAYS CHANGING, SO ACCELERATION IS OCCURING. THE ACCELERATION THAT
OCCURS IN CIRCULAR MOTION IS KNOWN AS CENTRIPETAL ACCELERATION.
A FORCE IS SIMPLY A PUSH OR A PULL. ALL FORCES HAVE BOTH SIZE AND DIRECTION.
SCIENTISTS EXPRESS FORCE USING A UNIT CALLED THE NEWTON (N).
THE NET FORCE IS THE FORCE THAT RESULTS FROM COMBINING ALL THE FORCES EXERTED ON AN
OBJECT.
IF FORCES ARE IN THE SAME DIRECTION, THEY CAN BE ADDED TOGETHER TO DETERMINE THE NET
FORCE.
IF FORCES ARE IN OPPOSITE DIRECTIONS, THE NET FORCE IS DETERMINED BY SUBTRACTING THE
SMALLER FORCE FROM THE LARGER ONE.
WHEN THE NET FORCE ON AN OBJECT IS NOT ZERO, THE FORCES ON THE OBJECT ARE
UNBALANCED. UNBALANCED FORCES PRODUCE A CHANGE IN MOTION.
UNBALANCED FORCES ARE NECESSARY TO CAUSE A NONMOVING OBJECT TO START MOVING.
WHEN THE FORCES APPLIED TO AN OBJECT PRODUCE A NET FORCE OF ZERO, THE FORCES ARE
BALANCED. BALANCED FORCES DO NOT CAUSE A NONMOVING OBJECT TO START MOVING.
FRICTION IS A FORCE THAT OPPOSES MOTION BETWEEN TWO SURFACES THAT ARE TOUCHING.
FRICTION OCCURS BECAUSE THE SURFACE OF ANY OBJECT IS ROUGH.
THE AMOUNT OF FRICTION BETWEEN TWO SURFACES DEPENDS ON MANY FACTORS, INCLUDING
THE ROUGHNESS OF THE SURFACES AND THE FORCE PUSHING THE SURFACES TOGETHER.
THE ROUGHER THE SURFACE, THE GREATER THE FRICTION.
IF FORCE IS INCREASED, THE FRICTION BETWEEN THE SURFACES IS INCREASED.
CHANGING THE AMOUNTS OF THE SURFACES THAT TOUCH DOES NOT CHANGE THE AMOUNT OF
FRICTION.
TYPES OF FRICTION
1)SLIDING FRICTION
2)ROLLING FRICTION
3)FLUID FRICTION
4)STATIC FRICTION
WHEN YOU PUSH AN ERASER ACROSS YOUR DESK, THIS IS CALLED SLIDING FRICTION.
THE FRICTION BETWEEN WHEELS AND THE FLOOR OF A DRESSER IS AND EXAMPLE OF ROLLING
FRICTION. THE FORCE OF ROLLING FRICTION IS USUALLY LESS THAN THE FORCE OF SLIDING
FRICTION.
FLUID FRICTION IS LESS THAN SLIDING FRICTION, THE TERM FLUID INCLUDES LIQUIDS, SUCH AS
WATER AND MILK, AND GASES SUCH AS AIR AND HELIUM.
FLUID FRICTION OPPOSES THE MOTION OF OBJECTS TRAVELING THROUGH A FLUID.
WHEN A FORCE IS APPLIED TO AN OBJECT BUT DOES NOT CAUSE THE OBJECT TO MOVE, STATIC
FRICTION OCCURS.
STATIC FRICTION DISAPPEARS AS SOON AS AN OBJECT STARTS MOVING, AND THEN ANOTHER
TYPE OF FRICTION IMMEDIATELY OCCURS.
WITHOUT FRICTION, A CAR IS USLESS.
LUBRICANTS ARE SUBSTANCES THAT ARE APPLIED TO SURFACES TO REDUCE THE FRICTION
BETWEEN THEM.
FRICTION CAN ALSO BE REDUCED BY SWITCHING FROM SLIDING FRICTION TO ROLLING FRICTION.
ANOTHER WAY TO REDUCE FRICTION IS TO MAKE SURFACES THAT RUB AGAINST EACH OTHER
SMOOTHER.
ONE WAY TO INCREASE FRICTION IS TO MAKE SURFACES ROUGHER.
ANOTHER WAY YOU INCREASE FRICTION IS TO INCREASE THE FORCE PUSHING THE SURFACES
TOGHTHER.
GRAVITY IS A FORCE OF ATTRACTION BETWEEN OBJECTS THAT IS DUE TO THEIR MASSES.
ALL MATTER HAS MASS. THEREFORE, ALL MATTER EXPERIENCES GRAVITY. THAT IS, ALL OBJECTS
EXPERIENCE AN ATTRACTION TOWARD ALL OTHER OBJECTS.
COMPARED WITH ALL THE OBJECTS AROUND YOU, EARTH HAS AN ENORMOUS MASS. THEREFORE,
EARTH'S GRAVITATIONAL FORCE IS VERY LARGE.
THE LAW OF UNIVERSAL GRAVITATION DESCRIBES THE RELATIONSHIPS BETWEEN GRAVITATIONAL
FORCE, AND DISTANCE.
THE LAW OF UNIVERSAL GRAVITATION STATES THE FOLLOWING: ALL OBJECTS IN THE UNIVERSE
ATTRACT EACH OTHER THROUGH GRAVITATIONAL FORCE. THE SIZE OF THE FORCE DEPENDS ON
THE MASSES OF THE OBJECTS AND THE DISTANCE BETWEEN THEM.
GRAVITATIONAL FORCE DECREASES AS DISTANCE INCREASES
WEIGHT IS A MEASURE OF THE GRAVITATIONAL FORCE EXERTED ON AN OBJECT.
MASS IS THE AMOUNT OF MATTER IN AN OBJECT, AND ITS VALUE DOES NOT CHANGE. IF AN OBJECT
IS MOVED TO A PLACE WITH A GREATER GRAVITATIONAL FORCE-LIKE JUPITER-ITS WEIGHT WILL
INCREASE, BUT ITS MASS WILL REMAIN THE SAME